# reference request – Maslov index equal to \$2\$ implies that the disk is not multiply covered

In the paper Floer cohomology of lagrangian intersections and pseudo-holomorphic disks in page $$1009$$ the authors claim that a map $$w:D^2rightarrow S^2$$ with $$w|_{partial D^2}subset L$$, where $$L$$ is the equator, and such that $$mu(w)=2$$, where $$mu$$ is the maslov index of the map, cannot be multiply covered and hence it will be injective in the interior of $$D^2$$.

I have tried proving this , but I am getting nowhere.

Any help or reference where I can look this up is appreciated, thanks in advance.